Photographic bleachjng-out layers



Patented Sept. l5, 1936 PATENT OFFICE 2,054,390 Pno'roGRArmcBLEAcmNG-OUT Lammev Ernst Rst, Zurich, Switzerland, and Andr Pulgar,Paris, France Apputauon August 29, 1934, serial No. '141,000v

l In Switzerland September 7, 1933 16 Claims.

This invention relates to the production of improved photographicbleaching out layers, that is to say, layers for the production ofpermanent images by the bleaching out process of color photography.

The great difliculty in the manufacture of bleaching out layersconsisted hitherto in that:-

(1) From a large number of dyestuffs there must be selected certain oneshaving parallel (simultaneous) bleaching capacity, requiring the samelength of time to bleach out to the same desired extent;

(2) A bleach-out sensitizer must be found, or rather a mixture ofsensitizers, which accelerates the bleaching out of the ycomponentsequally or vto the same'extent, i. e., according to nearly the samecharacteristic curves of degree of bleach attained with time. otherconditions being constant, and

(3) In addition to those requirements the mixture, before the exposure,must have a neutral shade so that the uncolored portion of the originaldoes not assume a color in the reproduction.

The fulfilment of the first two requirements alone was hithertoimpossible; the fulfilment of the third requirement even after thefulfilment of the first two is improbable since the dyestuils f havedifferent dyeing power.

It is the object of the present invention to provide a bleaching outlayer which is much more satisfactory than those hitherto known.

In the bleaching-out process of color photography, the fugitive dyes ofdifferent colors (as yellow, red, blue) which are incorporated in thesensitive bleach-out layer in a greyish mixture, bleach out under theaction of light of the same wave length which they respectively absorb,to leave the color to which the layer is exposed.

In this bleach-out process, there is often added one or more additionalsubstances as bleach-out sensitizers (also called acceptors), whosefunction is to increase (or diminish) the bleachingout reaction orsensitivity to bleaching-out of the several fugitive dyes applied to thematerial under exposure in the bleaching-out layer under the action ofthe light of the wave lengths which they respectively absorb. These"bleach-out sensitizers themselves are generally substantiallycolorless, such as allylthiourea, and in general are not themselvesdyes. l

One feature of this invention is based on the discovery that on plottinggraphically the time characteristics of bleaching out as the half valuetimes of the dyestuffs concerned as a function of the concentration ofthe bleach-out sensitizer,

it is possible to select suitable dyestufls for inclusion in a bleachingout layer, the curves of all of which approach each other very closelyor include only a small area. The half value time is the time in whichhalf of the quantity present 5 of a given dye is bleached out. Thusthree curves of red. yellow and blue dyestuifs, or fourcurves of yellow,orange, violet and green dyestuffs, or more curves corresponding to thenumber of dyestuffs used, may intersect at one point.

There is thus a bleach-out sensitizer concentration at which differentdyestuis bleach out to practically the same extent. At thisconcentration the bleaching out will have practically the same timecharacteristic even for the different exposure times and lightintensities after a certain minimum exposure. On this account it is alsopossible to employ such dyestufl's as hitherto did not receiveconsideration. although they possess -very valuable properties. Inaddition in 20 most cases it is possible to use only one bleachoutsensitizer.

Thus in accordance with one feature of this invention the dyestuffs forinclusion in a bleaching out layer are selected in the manner set out 25above and the bleach-out sensitizer is employed in the particularconcentration required.

As one example for the production of a bleaching out layer according tothis feature of theinvention, an emulsion is produced which is capable30 of being applied to paper and contains a deep violet mixture of thedyestuffs erythrosin, fluorescein and Victoria'blue in a totalconcentration of about 1%, the emulsion being sensitized as to bleachingout with 1.5% total concentration of 35 allyl-thiourea (also calledthiosinamine and allylthiocarbamide) as a bleach-out sensitizer. After atime of exposure in which a perceptible alteration in the dyestuffs canbe ascertained, there are obtained simultaneous similar bleaching outchar- 40 acteristics plotted against the time of exposure for thisparticular sensitizer concentration of the three diierent colored dyes.

- In another example a mixture of erythrosin, auramin and methylene blueis sensitized with about 3% of anethol. The importance of thisparticular selected value of concentration will be realized in this casewhen it is mentioned that on increasing the bleach-out sensitizerconcentration by 1% the bleaching out value for erythrosin varies byabout 30% although the values for the other two dyestuffs remainpractically the same.

In practice the theoretical value of the bleach- 55 are thus producedover the unexposed portionsl by means of the unchanged FeCla.

In addition to this action the additional substance may accelerate thebleaching of the dyestuft. In the above example the bleaching ofdyestulls is accelerated which bleach out by oxidation. On the otherhand by the bleaching the formation of FeClz is also accelerated.

The process is particularly suited to the manufacture of colorphoto-printing papers. In this case the dyestuffs can also be employedvery dilute since for technical printing merely an indication of thecolor shade is suilicient and the deep shades (for example black lines)are produced by the additional substance.

It has also been found that to produce black layers there can beemployed very advantageously diazo layers which can be developed dry,wet, or in a stream of gas.

In the manufacture, for example, of color vphoto-printing papers with adiazo compound as additional substance care must be taken that the raysof those wave lengths to which the diazo compound is sensitive penetratethe entire surface apart from entirely dark places. Unless theindividual fieldsof the surface act as very sharp color filters this isthe case. In this case the dyestuis of the photo-printing paper must besufficiently dilute and W'ell sensitized so that the gamma of the layeris sufliciently large, the graduation is thus sharp and the colorsaccordingly are sufficiently accurately reproduced.

The following example illustrates this feature of the invention:-

VNWith 20 grams of a diazo mixture hitherto customary for photo-printingpapers is admixed the following mixture:-

0.05 gram safranine GG 0.50 gram avinduline 0.08 gram of the compound ofthe indodicarbocyanine type. CH3 CH: CH3 CH3 C cin Br CH3 1.5 gramsallylthiourea, i. e., thiosinamin 30.0 grams 1% gelatin solution.

After complete solution, furthermore, 0.2 gram dimethylallyl-thiourea isadded. (With small variations of the concentration of this lattersubstance, adjustment can be made of the asynchronism of thecharacteristic of the dyestuff mixture, i. e., the non-parallelism ofthe characteristics of the different dyes, along the lines outlinedabove.) Finally the whole is diluted with a further 50 grams of hotwater.

The compound of the indodicarbocyanine type just mentioned is:10-bromo-lz1z3z3z3'z3 hexamethylindodicarbocyanine bromide, and itspreparation is described by Beattie et'al., Journal`of the ChemicalSociety (London), 1932, page 262.

The allylthiourea, as stated, is mixed with the dyestufs as a rstbleach-out sensitizer which -Will qualitatively. considerably increasethe sensitivity of the dyestuffs' to bleaching out, but without anyquantitative adjustments of the bleaching-out reactions of the differentdyes to close coincidence. The dimethylallylthiourea is subsequentlyadded as the adjusting sensitizer to facilitate adjusting to closecorrespondence for the different dyes the bleaching-out times requiredto attain a determined degree of bleach,

by modifying the characteristic curves of bleachout times againstsensitizer concentration required to obtain a determined degree ofbleach. In the above example also, the allylthiourea is less effectiveas a. sensitizer than the dimethylallylthiourea. Also, the allylthioureafacilitates the suspension and partial solution in water of thedimethylallylthiourea which by itself is practically insoluble inwater.l

The application can also take place without binding agent, thesubstances being wholly or partly dissolved. in organic solvents. Afterapplication they dry or crystallize out. The process can be carried outin such a. manner that only on moistening with water, or with the fixingagent or with the developer, is the fibre colored, l

that is to say it is not till this point that the colors are produced.

The same effect is attained when the dyestuffs are not dissolved but thewhole solid mass (dyestuffs and sensitizers) nely pulverized and rubbedinto the paper nbre.

The bleaching out layer rendered sufciently sensitive can veryadvantageously be employed for the copying of color films, in which casein some circumstances they can be employed for the same purpose withoutthe black auxiliary layer.

Having now particularly described and ascertained the naturel of oursaid invention and in what manner the same is to be performed, wedeclare that what We claim is:-

1. A bleach-out layer for color photography comprising a sensitive layercarrying a plurality of different dyes, said layer having incorporatedtherein a bleach-out sensitizer substantially in the concentrationdetermined as the value of sensitizer concentration for which thehalf-value bleaching-out times for the respective dyes most closelyapproach coincidence.

2. A bleach-out layer for color photography comprising a sensitive layercarrying a plurality of different dyes and having incorporated therein ableach-out sensitizer to which each of said dyes is sensitive, said dyesand said sensitizer being so Selected that the curves of half-'valuebleaching out times of the respective dyes plotted as a function of th-esensitizer concentration approach Very closely to meeting in a commonpoint, and said sensitizer being incorporated in said layersubstantially in the value of concentration for which said curves ofhalf-Value times most closely approach meeting in a common point.

3. A bleach-out layer for color photography comprising a sensitive layercarrying a plurality of different fugitive dyes respectively in ltheamounts which are optimum for the photographic subject to be reproducedWithout the employment of a bleach-out sensitizer, said bleach-out layerV wherein the dyes incorporated are thiazolinocarbocyanine salts.

7. A bleach-out layer according to claim 2,

in'g a plurality of diierent fugitive dyes and having incorporatedtherein a bleach-out sensitizer to which each of said dyes is sensitivesubstantially in the concentration for which the halfvalue bleaching-outtimes for the respective dyes most closely approach coincidence, andfurther comprising a separate control layer superposed on said firstnamed layer and having incorporated therein a light-sensitive substancewhich will be rendered black over the unexposed portions of said controllayer in the finished reproduction.

11. A'bleach-out layer according to claim 2, Whereinqthere isincorporated as an additional control agent a light-sensitive substancewhich under the process of developing will be rendered black over theunexposed portions of the layer.

12. In the manufacture of bleaching-out layers for color photographyfrom a base'sensitive layer, the process which consists in incorporatingin said sensitive layer a plurality of diierent fugitive dyes, adding todifferent test specimens of said layer a bleach-out sensitizer t whicheach-of said dyes is responsive as to bleaching successive- 1y invarying amounts, determining for which value of sensitizer concentrationthe half-value bleaching-out times for the respective dyes most closelyapproach coincidence, and incorporating in the production specimens ofsaid bleachingout layers said sensitizer in the concentration sodetermined. l

13. In the manufacture of bleaching-out layers for color photographyfrom a base sensitive layer, the process which consists in incorporatingin said sensitive layer a plurality of diierent fugitive dyes, adding todifferent test specimens of said layer a bleach-out sensitizer to whicheach'of said ldyes is responsive as to bleaching out suc.-

cessively in varying amounts, determining fory which value of sensitizerconcentration the halfvalue bleaching-out times for the respective dyesmost closely approach coincidence, incorporating in the productionspecimens of said bleaching-out layers said sensitizer in theconcentration so determined, and applying to said layer alight-sensitive compound which will be rendered black over the unexposedportions ofthe tive dyes, adding to diierent test specimens of saidlayer a bleach-out sensitizer to which each of said dyes is responsiveas to bleaching out successively in varying amounts, determining forwhich value of sensitizer concentration the halfvalue bleaching-outtimes for the respective dyes most closely approach coincidence,incorporating in the production specimens of said bleachingout layerssaid sensitizer in the concentration so determined, and applying ierricchloride to said layer. v

15. In the manufacture of bleaching-out layers for color photographyfrom a base sensitive layer, the process which consists in incorporating.in said sensitive layer a plurality of different fugitive dyes, addingto diierent test specimens of said layer a bleach-out sensitizer towhich each of said dyes is responsive as to bleaching out successivelyin varying amounts, determining for which value of sensitizerconcentration the halfvalue bleaching-out times for the respective dyesmost closely approach coincidence, incorporating in the productionspecimens of said bleachingout layers said sensitizer in theconcentration so determined, and applying an organic diazo compound tosaid layer. Y

16. In the manufacture of bleaching-out layers for color photographyfrom a base sensitive layer, the process which consists in incorporatingin said sensitive layer a plurality of different fugitive dyes, addingto diierent test specimens of said layer a bleach-out sensitizer towhich each of said dyes is responsive as to bleaching successively invarying amounts, determining for which value o f sensitizerconcentration the bleachingout times for the respective dyes required tolbleach out a determined substantial percentage of the quantity of dyespresent most closely approach coincidence, and incorporating in theproduction specimens of said bleaching-out layers said sensitizer in theconcentration so determined.

EaNs'r Rs'r. ANDR FOLGAR.

Sept. 15, 1936. SCHMIDT 2,054,391

MULTIPLE CYLINDERWEB DRIER Filed July 25, 1955

